An ISFET sensor is a field-effect transistor used for measuring ion concentrations in a solution. A typical ISFET sensor generally has a sensing layer (or gate insulator) having a surface in contact with the solution and an opposite surface in contact with a channel disposed between two electrodes, often referred to as the drain and the source, and a reference electrode (or gate electrode) in contact with the solution.
During use of the ISFET sensor, when the ion concentration (such as H+ or OH−) of the solution changes, the current flowing through the channel will change accordingly. Considering the nature of the ISFET, the ion sensitivity of the ISFET sensor will depend on the sensing layer as well as the composition of the channel disposed between the two electrodes. Some existing ISFET sensors harness the valuable electrical properties of graphene by providing the channel in the form of a graphene layer, in attempts to increase the ion sensitivity of the resulting ISFET sensor. However, although existing ISFET sensors are satisfactory to a certain degree, there still remains room for improvement.